250 miles into long distance trip, filled tank and 5 minutes later car stalled at 70 mph going downhill. After several tries, started and limped into a town,stalling occasionally. Suspecting bad gas at fillup, added a bottle of gas drier and car started and drove gingerly on 45 mph roads for an hour, then rejoined interstate. Car ran OK for next hour. After a rest stop, car started to hesitate occasionally and on every highway BUMP for 15 minutes, then ran well for next hour. Filled tank again andannded another bottle of drier. Car ran perfectly for next 2 hours until stopped at motel. Went out 15 minutes later for food and fuel and would not start on several tries. Noticed check engine light (may have been on before but obstructed view). Pulled intank pump fuse (have had success with this in past) and car started and drove for fillup and more drier. Next day reinstalled #4 fuse and car started and ran perfectly for next 3 hours until pulled into local traffic. Stalled several times, and eventually would not restart (turned over but wouldn't catch). Had to have towed (only second time in 25 years of driving 240s). I wasn't travelling with Bentley manual and accidentally pulled up Canada's 240 diagnostic test which puts probe in #6 instead of #2. Got code 2-1-4 (intermittent signal from rpm sensor), which actually does make sense. After the towing I was able to drive 1/2 mile from a closed indy shop to a motel, and cleared code. No code on restart and drove back to shop next day to leave there. Shop is replacing rpm sensor (with used, new not available readily) at my instruction (from my incorrectly done diagnostic test).

Bad gas seems a given due to quick response to drier, but will it mess up O2 sensor? Failing pre-pump? Any ideas. Scheduled to pick it up in morning unless more needs to be done.